Signal receiver



S IGN AL RECEIVER Filed April 23, 19-31 Patented F eb. 27, 1934 UNITED STATES PATENT OFFICE SIGNAL RECEIVER Application April 23, 1931, Serial No. 532,310 In Sweden April 29, 1930 2 Claims.

The present invention has for its object a device for receiving alternating current signals. More particularly the invention relates to such devices in which a receiving relay is included in the anode circuit of an electronic valve rectifier. It has for its object to eliminate the inconvenience occurring in such receivers that the time required for the receiving relay to attract its armature fluctuates considerably with the intensity of the incoming signals. In hitherto known receiving devices of this kind the electronic valve rectifier is usually adapted to operate with anode bend rectification. Upon the grid there is then impressed a negative grid bias- 5 ing voltage of such a value that the rectifier is operating at the lower bend of the characteristic. The anode current will then be zero or nearly zero so long as no signals are incoming and assumes, upon the reception of a signal, a

positive value which is the higher the higher the amplitudes of the incoming oscillations are. The current through the winding of the receiving relay will then reach its stationary value the more rapidly the greater the amplitude of oscillation is. For this reason the receiving relay attracts its armature considerably more quickly upon the receipt of a powerful signal than upon the receipt of a weak signal. After the termination of the incoming signal the anode current decreases to the value, at which the relay drops its armature, the more quickly the smaller the oscillation amplitude is. The duration of the signal or telegraph sign thus becomes the shorter the less the signal intensity is. The signal intensity is in turn dependent upon the resistance and leakage of the line which properties, as known, may be subjected to considerable variations daily on account of changes in the weather or in the temperature. For this reason the durations of the telegraph signs may fluctuate considerably whereby faults in the telegraphic communication may occur.

According to the present invention the durations of the signs may be made independent of the signal intensity in that the electronic valve rectifier is adapted to operate with two mutually opposite rectifying actions, i. e. with anode rectification changing the anode current in a positive direction and also grid rectification tending to to change the anode current in opposite direction. Upon receiving comparatively weak signals, the valve substantially operates only with anode rectification whereas said valve, if the intensity of the signal exceeds a certain limit,

will also operate with grid rectification and thereby compensates the increase in anode current corresponding to the increase in signal intensity. By this disposition it is rendered possible to attain that the amperage of the anode current always assumes substantially the same value for an incoming signal independently of the signal intensity provided, the signal, however, has a suflicient intensity to cause grid currents.

The invention will be more closely described with reference to the accompanying drawing. Figure l is a circuit diagram of an embodiment of a receiver according to the present invention. Figure 2 shows another embodiment. Figure 3 is a current diagram illustrating the increase in Y0 anode current upon the receipt of incoming signals of different intensities in an ordinary receiver of the kind in question. Figure 4 shows the relation between the anode current and the amplitude of the supplied alternating current in the connection according to Figure 1. Figure 5 is a current diagram corresponding to that of Figure 3 and relating to a receiver according to the invention.

Figure 3 shows the effects of two signals A and l B incoming to an ordinary receiving device as hitherto used which signals have the same duration S but different intensities. The signal is in each case assumed to enter the device at the time to and to cease at the time ts. On account of the self induction in the receiving relay the anode current does not immediately reach its full value and it does not decrease at once to the zero value upon the termination of the signal. Upon receipt of the stronger signal A, the anode current ia rises comparatively rapidly and reaches at the time tAo the value ii at which the receiving relay is caused to attract its armature. The anode current then rises considerably beyond this current value. Upon the incoming signal ceasing at the time ts the anode current decreases comparatively slowly and not until at the time ta; it will have dropped to that value z'z at which the relay drops its armature. Therefore the duration of the received signal will be which is reached at the time is... The resulting duration of the signal will be in this case This duration is considerably shorter than that of the stronger signal for the reason that the weaker signal begins later and ceases earlier.

In the arrangement shown in Figure 1 the grid circuit of the electronic valve rectifier is, according to the invention, connected to the incoming line over an input transformer T and includes between the secondary of the input transformer and the grid a grid leak R and a condenser C parallel connected thereto. The grid circuit includes furthermore a direct current battery G impressing upon the grid a negative grid biasing voltage of such a value that the anode current normally will be zero or only of an insignificant value. The anode circuit includes a direct current relay Re in series with the anode battery H. If the amplitude of the incoming oscillations is so small that no grid current is caused the valve operates as an ordinary anode rectifier at the lower bend of the characteristic. If the incoming signals have such intensities that grid current starts to flow the anode rectification is combined with a grid rectification operating in opposite direction, because the grid biasing voltage is further reduced by the drop of voltage caused by the grid current in the grid leak B. This displacement of thegrid biasing voltage in a negative direction increases in accordance with the increase in the amplitudes of oscillations. The result will be that the amplitudes of the rectified current impulses in the anode circuit are unable to exceed to any considerable degree the value corresponding to that amplitude of oscillation at which grid current starts to flow. The amperage of the rectified current will be practically independent of the signal intensity provided said intensity exceeds the above mentioned minimum value at which grid current just begins to fiow. This condition is illustrated in Figure 4- showing the relation between the anode current is and the alternating current voltage V- between the secondary terminals of the input transformer T. As seen from the figure the intensity of the rectified current rises in the beginning rapidly with the amplitude of the alternating current voltage until the latter has reached the value V- which is substantially equal to or somewhat greater than, the absolute value of the negative grid biasing voltage. Upon a further increase of the amplitude of the alternating current voltage the anode current rises only very slowly. The characteristic course of the curve in Figure 4 depends upon the above mentioned condition that grid current begins to flow when the amplitude of the alternating current voltage reaches or exceeds the value V-.

Figure 5 representing a current diagram corresponding to that of Figure 3 and relating to the device according to Figure 1 shows the variation of the current in the anode circuit for two incoming signals having the same duration S but mutually considerably diiierent intensities. The signal having the duration S is assumed, as before, to enter the grid circuit at the time to and to cease at the time ts. The time if at which the anode current for the stronger signal A rises to the value i1 required for the attraction of the receiving relay is only slightly earlier than the time tBo when the anode current on account of the weaker signal 13' has reached the same value. The received signal begins therefore near- 1y simultaneously in both cases. The coincidence between the points of time corresponding to the ceasing of the two signals A B is still more apparent and the duration of the received signal will be practically constant independent of the intensity,.of the incoming signal on the condition, however, that the amplitude of the weakest signal occurring is at least equal to V-.

The amplitude of the incoming signals may be 1 adjusted by means of a potentiometer P, Figs. 1, 2, in such a manner that this condition is complied with.

The condenser C having for its essential purpose to form a path for the oscillations past the grid leak R may in certain cases be omitted. The resistance R should be high and the capacity of the condenser C small although considerably higher than the capacity between grid and cathode. To allow a suflicient time for the condenser C to discharge between the different telegraph signs the relation between R and C should be so selected that RC is less than where wt is the so called point frequency, 1. e. the number of points per second in a certain definite telegraph rapidity, provided only points are sent.

In the embodiment according to Figure 2 the incoming signal is supplied to the electronic valve through the intermedium of a special rectifier device comprising a glow tube or a neon tube or other glow discharge device g, a condenser C1, and an auxiliary current source, all connected in series with the secondary winding of the transformer T. The condenser C1 together with an ohmic resistance R1 shunted therewith is connected to the input side of the electronic valve in series with the resistance R and the grid battery G..

The auxiliary current source consists of a part of the anode battery H-of the electronic valve relay and the grid biasing battery G and it has a voltage being slightly lower than the lighting voltage and the discharge voltage of the glow tube g which voltages for the sake of simplicity are assumed to be equal. So long as no oscillations are received the glow tube a forms a complete interruption and the grid in the electronic valve has, as in the case above described, a negative grid biasing voltage of such a value that the anode current is substantially zero.

If now oscillations are received, the amplitudes Vs of which are greater than the difi'erence between the lighting voltage Vt of the glow tube and the voltage V0 of the auxiliary current source the glow tube is lighted once for each positive half wave i. e. for each half wave having the same direction as the auxiliary voltage V0 and the condenser C1 is then charged up to a voltage the upper condenser coating being then positively charged.

When the alternating voltage falls below the j aninsignificant amount before the glow tube is lighted the next time when the condenser voltage is again raised. As is readily understood, the condenser voltage can never exceed the value V0 however great the amplitude of the signal 05- I cillation is.

vented from exceeding that value which corresponds substantially to zero potential of the grid.

I claim: 1. An arrangement for receiving alternating current telegraph signals comprising in combination, a thermionic valve rectifier, a direct current relay responsive to a predetermined mini-- mum strength of current in the anode circuit of said valve, a direct current source in the grid circuit of the valve impressing a negative grid biasing voltage on the grid so as to reduce normally the anode current substantially to zero, a grid leak in series with said battery and dimensioned so as to produce, under the influence of incoming oscillations of an amplitude exceeding a certain predetermined value, a grid rectification counter-acting the anode rectification and a condenser shunted across said grid leak.

2. An arrangement for receiving alternating current telegraph signals comprising in combination, a thermionic valve rectifier, a direct current relay responsive to a predetermined minimum strength of current in the anode circuit of Said valve, a direct current source in the grid circuit of the valve impressing a negative grid biasing voltage on the grid so as to reduce normally the anode current substantially to zero,

a grid leak in series with said battery and dimensioned so as to produce, under the influence of in-- coming oscillations of an amplitude exceeding a certain predetermined value, a grid rectification counteracting the anode rectification, a first condenser shunted across said grid leak, a second condenser inserted in the grid circuit in series with the grid leak, an input circuit comprising a glow lamp and a battery in series and connected in parallel with said second condenser.

MAURITZ V08. 

